Remark 3.2 We note here that what we here call positive semi-definite functions are sometimes referred to as positive semi-definite kernels, e.g. in [1]}, [2]}, [3]}. Our terminology stems from e.g. [4]} and refers to functions of \(2n\)  complex variables. These functions should not be confused with positive semi-definite functions in the sense of e.g. [3]}, which refers to functions of one real variable.

